you're have to check that the brake cables are releasing all the way. Best thing to do is when you think it is going to act up is to jack up the rear end and then release the parking brake. check both rear wheels to see if they are both stuck or is it just one side. Also, how do you know it's the rear that is hanging up? Sometimes the front calipers can stick and it may feel like the parking brake. If when you chcek the rear wheels and they both spin and are not locked up, jack up the front and see if one or both of the front wheels are stuck.